Water-in-oil emulsion composition for forming silicone elastomer porous material

ABSTRACT

A method for preparing a silicone elastomer porous material includes the steps of (1) providing a water-in-oil emulsion including a liquid silicone rubber material which forms a silicone elastomer upon curing, a silicone oil material that has a surface activation function, and water droplets dispersed in the liquid silicone rubber material, (2) subjecting the emulsion to a primary heating, thereby curing the liquid silicone rubber material to form a silicone elastomer and confining the water droplets within the silicone elastomer substantially as they are present in the emulsion, and (3) subjecting the silicone elastomer to a secondary heating, thereby evaporating and removing the water droplets from the silicone elastomer, thereby forming the silicone elastomer porous material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. Application Ser.No. 10/986,659 filed on Nov. 12, 2004, which is based upon and claimsthe benefit of priority from prior Japanese Patent Application No.2003-391144, filed Nov. 20, 2003, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a water-in-oil emulsion composition forforming a silicone elastomer porous material, and more specifically to awater-in-oil emulsion composition which can produce a silicone elastomerporous material without being accompanied by a foaming phenomenon.

2. Description of the Related Art

Silicone elastomer porous materials are used in a variety of fields, forexample, as parts of image forming devices such as photocopiers andlaser printers, including developing rollers, toner feeding rollers,transfer rollers and drum cleaning rollers, as sheet feeding rollers ofphotocopiers, various types of printers and plotters, and as pressurerollers of fixing devices.

Conventionally, porous materials are produced mainly by utilizingfoaming phenomenon. For foaming, a chemical foaming agent, a gas orwater has been used as a foaming agent. The manufacture of siliconeelastomer porous materials is not exception, and in most cases, siliconeelastomer porous materials have been prepared by using one of thesefoaming agents. However, in such a conventional method of producing asilicone elastomer porous material, curing of silicone rubber andfoaming are effected at simultaneously, with the result that cells(pores) in the resultant porous material are not uniform in size andtheir sizes vary in a wide range. Further, it is conventionallydifficult to form cells having a size as small as, for example, 20 μm orless.

On the other hand, Jpn. Pat. Appln. KOKAI Publication No. 6-287348discloses a method of producing a silicone elastomer porous material byfreezing a room-temperature curing polysiloxane emulsion containing apolysiloxane having a silanol group, a specific crosslinking agent, acuring catalyst, and an emulsifying agent by refrigeration andsublimating the water to dry the frozen emulsion without defrosting it.Even with this method, it is still difficult to produce a porousmaterial having uniform and fine cells. Further, the porous materialobtained by this method is of an open cell type.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a water-in-oil emulsioncomposition from which a silicone elastomer porous material having evenand fine-sized cells (pores) can be produced without being accompaniedby a foaming phenomenon.

According to an aspect of the present invention, there is provided awater-in-oil emulsion composition for forming a silicone elastomerporous material, comprising a liquid silicone rubber material whichforms a silicone elastomer upon curing, a silicone oil material whichhas a surface activation function, and water.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a graph showing the water separation ratio of each ofemulsions prepared in Experiment 1, which will be explained below indetail;

FIG. 2 is a graph showing the water separation ratio of each ofemulsions prepared in Experiment 2, which will be explained below indetail;

FIG. 3 is a graph showing the water separation ratio of each ofemulsions prepared in Experiment 2, which will be explained below indetail;

FIG. 4 is a graph showing the water separation ratio of each ofemulsions prepared in Experiment 3, which will be explained below indetail;

FIG. 5 is a graph showing the water separation ratio of each ofemulsions prepared in Experiment 4, which will be explained below indetail;

FIG. 6 is a graph showing the water separation ratio of each ofemulsions prepared in Experiment 5, which will be explained below indetail;

FIG. 7 is a graph showing the water separation ratio of each ofemulsions prepared in Experiment 6, which will be explained below indetail;

FIG. 8 is a graph showing the water separation ratio of each ofemulsions prepared in Experiment 7, which will be explained below indetail;

FIG. 9 is a graph showing the water separation ratio of each ofemulsions prepared in Experiment 8, which will be explained below indetail;

FIG. 10 is a graph showing the water separation ratio of each ofemulsions prepared in Experiment 9, which will be explained below indetail;

FIG. 11 is an SEM photograph showing a cross section of a siliconeelastomer porous material produced in Example 1, which will be explainedbelow in detail;

FIG. 12 is an SEM photograph showing a cross section of a siliconeelastomer porous material produced in Example 2, which will be explainedbelow in detail; and

FIG. 13 is an SEM photograph showing a cross section of a formed bodyproduced in Comparative Example 1, which will be explained below indetail.

DETAILED DESCRIPTION OF THE INVENTION

A water-in-oil emulsion composition according to the present inventioncomprises a liquid silicone rubber material which forms a siliconeelastomer upon curing, a silicone oil material which has a surfaceactivation function, and water.

The liquid silicone rubber material is not particularly limited as longas it forms a silicone elastomer upon curing by heating; however, it ispreferable to use a so-called addition reaction curing liquid siliconerubber. The addition reaction curing liquid silicone rubber contains apolysiloxane having unsaturated aliphatic group or groups, acting as amain agent, and an active hydrogen-containing polysiloxane acting as acrosslinking agent. In a polysiloxane having unsaturated aliphaticgroups, the unsaturated aliphatic group is introduced at the respectiveterminals of the molecule, and they can be introduced as side chains aswell. Such a polysiloxane having the unsaturated aliphatic groups can berepresented by, for example, the following formula (1):

In the formula (1), each R¹ represents an unsaturated aliphatic group,and each R² represents a C₁-C₄ lower alkyl group, a fluorine-substitutedC₁-C₄ lower alkyl group or a phenyl group. The sum of a and b is usually50 to 2,000. The unsaturated aliphatic group represented by R¹ isusually vinyl group. R² is usually methyl group.

The active hydrogen-containing polysiloxane (hydrogen polysiloxane)serves as a crosslinking agent for the polysiloxane having unsaturatedaliphatic groups, and has a hydrogen atom (active hydrogen) bonded to asilicon atom in its main chain. It is preferable that three or morehydrogen atoms is present per molecule of the active hydrogen-containingpolysiloxane. Such an active hydrogen-containing polysiloxane can berepresented by, for example, the following formula (2):

In the formula (2), each R³ represents hydrogen or a C₁-C₄ lower alkylgroup, and each R⁴ represents a C₁-C₄ lower alkyl group. The sum of cand d is usually 8 to 100. The lower alkyl groups represented by R³ andR⁴ are usually methyl groups.

These liquid silicone rubber materials are commercially available. Itshould be noted that as the products on the market, the polysiloxanecontaining unsaturated aliphatic groups, constituting an additionreaction curing liquid silicone rubber, and the activehydrogen-containing polysiloxane are provided in separate packages, anda curing catalyst necessary to cure both of these polysiloxanes, whichwill be later described in detail, is added to the activehydrogen-containing polysiloxane package.

The silicone oil material having a surface activation function serves asa dispersion stabilizer for stably dispersing water in emulsion. Thus,the silicone oil material having a surface activation function exhibitsan affinity for water as well as for the liquid silicone rubbermaterial. It is preferable that this silicone oil material has ahydrophilic group such as an ether group. Further, the silicone oilmaterial exhibits an HLB value of usually 3 to 13, preferably 4 to 11.More preferably, two ether-modified silicone oils having HLB valuesdifferent from each other by 3 or more are used in combination. In thiscase, still more preferably, a first ether-modified silicone oil havingan HLB value of 7 to 11 and a second ether-modified silicone oil havingan HLB value of 4 to 7 are used in combination. Either one of theether-modified silicone oils may be of a type in which a polyether groupis introduced at a side chain of the polysiloxane, which can berepresented by, for example, the following formula (3):

In the formula (3), each R⁵ represents a C₁-C₄ lower alkyl group, and R⁶represents a polyether group. The sum of e and f is usually 8 to 100.The lower alkyl group represented by each R⁵ is usually a methyl group.Further, the polyether group represented by R⁶ usually includes(C₂H₄o)_(x) group, (C₃H₆O)_(y) group or (C₂H₄O)_(x)(C₃H₆O)_(y) group.The HLB value is determined mainly by the values of x and y. Theseliquid silicone oil materials having a surface activation function arecommercially available.

Needless to say, in the water-in-oil emulsion of the present invention,water is dispersed in the form of particles (droplets) as adiscontinuous phase. As will be described later in detail, the diameterof droplets of water substantially determines the diameter of the cells(pores) of the porous material obtained from the water-in-oil emulsionof the present invention. Water can exist in the form of droplets havingan average diameter of 1 to 50 μm. Especially, in the water-in-oilemulsion of the present invention, water droplets having a diameter of20 μm or less can exist to occupy 90% or more of all the water droplets.The size of water droplets in the emulsion can be measured bymicroscopic observation.

In order to cure the liquid silicone rubber material, the water-in-oilemulsion of the present invention may contain a curing catalyst. As thecuring catalyst, a platinum catalyst can be employed as is known in theart. It suffices that the amount of the platinum catalyst is about 1 to100 ppm by weight in terms of platinum atom. The curing catalyst may beadded to the water-in-oil emulsion of the present invention whenproducing a silicone elastomer porous material, or it may be blendedwhen preparing the emulsion.

In order to obtain a water-in-oil emulsion with a particularly excellentwater dispersion stability, it is preferable that 0.2 to 5.5 parts byweight of the silicone oil material having a surface activationfunction, and 10 to 250 parts by weight of water are used based on 100parts by weight of the liquid silicone rubber material. In the casewhere the silicone oil material having a surface activation function iscomposed of a combination of the first ether-modified silicone oil andthe second ether-modified oil, described above, it is preferable that0.15 to 3.5 parts by weight of the first ether-modified silicone oil and0.05 to 2 parts by weight of the second ether-modified silicone oil (atotal of 0.2 to 5.5 parts by weight) are used based on 100 parts byweight of the liquid silicone rubber material. In the case where theliquid silicone rubber material is composed of a combination of apolysiloxane having unsaturated aliphatic groups and an activehydrogen-containing polysiloxane, the ratio between the former andlatter in weight is preferably 6:4 to 4:6.

The water-in-oil emulsion of the present invention may contain varioustypes of additives depending on the use of the porous material obtainedtherefrom. Examples of the additives are colorants (such as pigments anddyes), electrical conductivity-imparting agents (such as carbon blackand metal powder) and fillers (such as silica). Further, thewater-in-oil emulsion of the present invention may contain a lowmolecular-weight, non-reactive silicone oil in order to adjust theviscosity of the emulsion for the purpose of, for example, easilyperforming defoaming of the emulsion. When the water-in-oil emulsion ofthe present invention has a viscosity of 1 cSt to 200,000 cSt, it can beeasily defoamed and therefore it can be handled conveniently.

The water-in-oil emulsion of the present invention can be prepared byvarious methods. In general, it can be prepared by mixing the liquidsilicone material, silicone oil material having a surface activationfunction and water together with an additive if necessary, and stirringthe mixture sufficiently. In the case where the liquid silicone rubbermaterial is provided by a combination of the polysiloxane containingunsaturated aliphatic groups and the active hydrogen-containingpolysiloxane, the polysiloxane containing unsaturated aliphatic groupsand a portion of the silicone oil material having a surface activationfunction can be mixed together and stirred to obtain a first mixture,whereas the active hydrogen-containing polysiloxane and the rest of thesilicone oil material having a surface activation function can be mixedtogether and stirred to obtain a second mixture. Subsequently, whilemixing and stirring the first mixture and the second mixture, water canbe gradually added thereto, and the mixture can be stirred to prepare adesired emulsion. Needless to say, the method of preparing thewater-in-oil emulsion of the present invention is not limited to theabove one. The order of addition of the liquid silicone rubber material,silicone oil material having a surface activation function, water andadditives that might be added as needed may be arbitrary. The stirringfor forming the emulsion can be carried out using an agitator at arotation speed of, for example, 300 rpm to 1,000 rpm. After theformation of the emulsion, the emulsion can be subjected to a defoamingprocess without heating it, using, for example, a vacuum decompressor,so as to remove the air present in the emulsion.

In order to produce a silicone elastomer porous material using thewater-in-oil emulsion of the present invention, the water-in-oilemulsion of the present invention is subjected to a heat curing (primaryheating) condition for the liquid silicone rubber material in thepresence of a curing catalyst. In the primary heating, it is preferableto use a heating temperature of 130° C. or less in order to thermallycure the liquid silicone rubber material without evaporating the waterin the emulsion. The heating temperature for the primary heating isusually 80° C. or higher, and the heating time is usually about 5minutes to 60 minutes. By this primary heating, the liquid siliconerubber is cured, and confines the water droplets in the emulsion as theyare present in the emulsion. The cured silicone rubber is cured to sucha degree that it can withstand the expanding force exerted by the waterwhen the water is evaporated by a secondary heating, which will bedescribed below.

Next, in order to remove the water from the cured silicone rubberconfining the water droplets therein, a secondary heating is carriedout. The secondary heating is preferably carried out at a temperature of70° C. to 300° C. If the heating temperature is lower than 70° C., itwould take an excessively long time to remove the water, whereas if thetemperature exceeds 300° C., the cured silicone rubber may be degraded.With the heating temperature of 70° C. to 300° C., the water is removedby evaporation within 1 to 24 hours. By the secondary heating, the watercontent is removed by evaporation, and further the final curing of thesilicone rubber material can be effected. The water removed byevaporation leave cells having a diameter substantially the same as thatof the water droplets, in the cured silicone rubber material (siliconeelastomer).

In this way, the water-in-oil emulsion of the present invention canproduce a silicone elastomer without being accompanied by a foamingphenomenon. The water droplets within the emulsion are confined in thecured silicone rubber by the primary heating, and then they simplyevaporate in the secondary heating. In this manner, a substantiallyclosed-cell silicone elastomer porous material can be obtained. Theporous material obtained is very fine in cells (pores) and has a narrowdistribution of cell sizes, and thus the cells are highly uniform. Thesilicone elastomer porous material produced from the water-in-oilemulsion of the present invention can be utilized in various fields. Forexample, the porous material can be used as parts of image formingdevices such as photocopiers and laser printers, including developingrollers, toner feeding rollers, transfer rollers and drum cleaningrollers, as sheet feeding rollers of photocopiers, various types ofprinters and plotters, and as pressure rollers of fixing devices.

The present invention is further described below by way of its Examples,but the invention is not limited to these Examples.

First, for the purpose of obtaining the optimal ratio between the liquidsilicone rubber material, silicone oil material having a surfaceactivation function (a dispersion stabilizer for water) and water, inorder to prepare a water-in-oil emulsion excellent in waterdispersibility, the following Experiments 1 to 5 were carried out.Further, for the purpose of obtaining the optimal HLB value of thedispersion stabilizer, the following Experiments 6 to 9 were carriedout.

Since the liquid silicone rubber material used in the present inventioncures, dimethylsilicone oil (KF-96 available from Shin-Etsu ChemicalCo., Ltd (viscosity: 100 cSt)), which is non-reactive (non-curable)straight silicone oil that has a chemical structure similar to that ofthe curable liquid silicone rubber, was used in Experiments 1 to 9 inplace of this curable liquid silicone rubber for ease of handling.

In Experiments 1 to 5, two types of polyether-modified silicone oils(KF-618 available from Shin-Etsu Chemical Co., Ltd (HLB value: 11);“dispersion stabilizer I” in Experiments 1 to 5) and (KF-6015 availablefrom the same company (HLB value: 4); “dispersion stabilizer II” inExperiments 1 to 5) were used as the dispersion stabilizer.

On the other hand, in Experiments 6 to 9, the aforementioned KF-6015(HLB value: 4; “dispersion stabilizer A” in Experiments 6 to 9), KF-352(HLB value: 7; “dispersion stabilizer B” in Experiments 6 to 9), KF-353(HLB value: 10; “dispersion stabilizer C” in Experiments 6 to 9), theaforementioned KF-618 (HLB value: 11; “dispersion stabilizer D” inExperiments 6 to 9), and KF-354L (HLB value: 16; “dispersion stabilizerE” in Experiments 6 to 9), which are polyether-modified silicone oilsavailable from Shin-Etsu Chemical Co., Ltd, were used as the dispersionstabilizers.

According to the product catalog, all of these polyether-modifiedsilicone oils have a structure represented by the above formula (3) inwhich each R⁵ is a methyl group, and R⁶ has (C₂H₄O)_(x)(C₃H₆O)_(y) groupas a polyether group.

PROCEDURES OF EXPERIMENTS

Water, dimethylsilicone oil and two dispersion stabilizers are gentlypoured into a predetermined container in this order, and allowed tostand still for a predetermined time. The water, the dimethylsiliconeoil and the dispersion stabilizers are separated into three layers, andthe thickness t₁ of the water layer is measured. Next, the contents inthe container are stirred with a hand mixer to form an emulsion. Afterthe formation of the emulsion, the emulsion is allowed to stand still,during which the thickness t₂ of the layer of water separated from theemulsion is measured for every predetermined time elapse. The rate ofseparation of water (water separation rate) (%) is calculated from theequation: (t₂/t₁)×100. As evaluation, cases where the water separationrate after 20 minutes satisfies a criterion of 50% or less are indicatedby ◯, whereas cases where it does not satisfy the standard are indicatedby X . In consideration of the time required for the emulsion to bestable after being formed until poured into a mold, it is preferablethat the water separation rate of the emulsion from the time when it isformed until an lapse of time of 20 minutes is 50% or less. Such astable emulsion can stably produce a silicone elastomer porous materialof a higher quality.

It should be noted that in FIGS. 1 to 9, which show the results ofExperiments 1 to 9, the numeral added to the respective curve indicatesthe Formulation number in the respective Experiment. For example, theresult of Formulation 1 is indicated by Curve 1. Further the compositionof each Formulation is based on parts by weight.

Experiment 1

As shown in Table 1 below, various emulsions (Formulations 1-4) wereprepared in which the ratio between dispersion stabilizer I anddispersion stabilizer II was varied while fixing the total amount ofthese at constant, with the ratio and the total amount ofdimethylsilicone oil and water fixed at constant. For each emulsion, thewater separation rate was measured at various lapses of times. The waterseparation rate was also measured on an emulsion (Formulation 0) thatwas prepared without using any dispersion stabilizers. The results areshown in Table 2 below and FIG. 1, and the results of evaluation areshown also in Table 1. It should be noted that in Formulation 5, aportion of the oil gelled. In Table 2, the symbol “*” indicates that theboarder of the separated water layer was not clear (same applies toTables 4, 6, 8, 10, 13, 15 and 17 below.)

From the results shown in Table 1 and FIG. 1, it can be understood thatin the case where dimethylsilicone oil and water are used at a ratio of50:50, an emulsion with a desirable water dispersion stability can beobtained if the ratio between dispersion stabilizer I and dispersionstabilizer II is 5:5 to 7:3. TABLE 1 Compositions of Formulations 0-5and the Results of Evaluation Form. Form. Form. Form. Form. Form. 0 1 23 4 5 Dimethyl- 50 50 50 50 50 50 silicone oil Water 50 50 50 50 50 50Dispersion 0 1 0.7 0.5 0.3 0 stabilizer I Dispersion 0 0 0.3 0.5 0.7 1stabilizer II Evaluation X X ◯ ◯ X X

TABLE 2 Water Separation Rates of Formulations 0-4 Water Separation Rate(%) After After After After After After After After After After 0.5 min.1 min. 2 min. 3 min. 5 min. 7 min. 10 min. 12 min. 15 min. 20 min. Form.0 0.0 59.6 67.7 78.5 87.8 89.4 94.8 94.8 94.8 94.8 Form. 1 0.0 5.5 9.816.4 24.6 38.3 41.0 43.8 49.2 54.7 Form. 2 0.0 * * * 5.5 8.2 10.9 16.416.4 16.4 Form. 3 0.0 * * * * 8.2 16.4 21.9 21.9 21.9 Form. 4 0.0 10.932.8 54.7 76.6 82.1 84.8 84.8 84.8 87.5

Experiment 2

As shown in Table 3 below, various emulsions (Formulations 6-14) wereprepared in which the total amount of dispersion stabilizer I andstabilizer II was varied while fixing the ratio between these atconstant, with the ratio and the total amount of dimethylsilicone oiland water fixed at constant. For each emulsion, the water separationrate was measured. The results are shown in Table 4 below. The resultsof Formulations 6 to 9 are also shown in FIG. 2 and those ofFormulations 10 to 14 are also shown in FIG. 3. The evaluation of eachof the emulsions is indicated also in Table 3.

From the results shown in Table 3 and FIGS. 2 to 3, it can be understoodthat Formulations 7 to 10 produce emulsions with a desirable waterdispersion stability. TABLE 3 Compositions of Formulations 6-14 and theResults of Evaluation Blend Blend Blend Blend Blend Blend Blend BlendBlend 6 7 8 9 10 11 12 13 14 Dimethyl- 50 50 50 50 50 50 50 50 50silicone oil Water 50 50 50 50 50 50 50 50 50 Dispersion 0.175 0.350.525 0.7 1.4 3.5 7 14 21 stabilizer I Dispersion 0.075 0.15 0.225 0.30.6 1.5 3 6 9 stabilizer II Total amount 0.25 0.5 0.75 1 2.0 5 10 20 30of Dispersion stabilizers Evaluation X ◯ ◯ ◯ ◯ X X X X

TABLE 4 Water Separation Rates of Formulations 6-14 Water SeparationRate (%) After After After After After After After After 0.5 min. 3 min.5 min. 7 min. 10 min. 12 min. 15 min. 20 min. Form. 6 0.0 10.9 16.4 21.927.4 32.8 32.8 43.8 Form. 7 0.0 13.7 13.7 19.1 24.6 27.4 28.4 32.8 Form.8 0.0 8.2 10.9 13.7 16.4 21.9 24.6 27.4 Form. 9 0.0 * 5.5 8.2 10.9 16.416.4 16.4 Form. 10 0.0 * 8.2 10.7 13.7 16.4 19.1 19.1 Form. 11 0.0 * * *10.9 16.4 30.1 43.8 Form. 12 0.0 * * * 8.2 16.4 35.6 54.7 Form. 130.0 * * * 8.2 13.7 27.4 54.7 Form. 14 0.0 * * * * * 43.8 62.9

Experiment 3

As shown in Table 5 below, various emulsions (Formulations 15-19) wereprepared in which the ratio between dimethylsilicone oil and water wasvaried while fixing the total amount of these was fixed at constant,with the ratio and the total amount of dispersion stabilizer I andstabilizer II fixed at constant. For each emulsion, the water separationrate was measured. The results are shown in Table 6 below and FIG. 4.The evaluation of each of the emulsions is shown also in Table 5.

From the results shown in Table 6 and FIG. 4, it can be understood thatas the ratio of water is higher, the dispersion property of water islowered. It can be further understood that Formulations 17 to 19 produceemulsions with a desirable water dispersion stability. TABLE 5Compositions of Formulations 15-19 and the Results of Evaluation Form.Form. Form. Form. Form. 15 16 17 18 19 Dimethyl- 10 30 50 70 90 siliconeoil Water 90 70 50 30 10 Dispersion 0.7 0.7 0.7 0.7 0.7 stabilizer IDispersion 0.3 0.3 0.3 0.3 0.3 stabilizer II Evaluation X X ◯ ◯ ◯

TABLE 6 Water Separation Rates of Formulations 15-19 Water SeparationRate (%) After After After After After After After After After After 0.5min. 1 min. 2 min. 3 min. 5 min. 7 min. 10 min. 12 min. 15 min. 20 min.Form. 15 0.0 * * * 109.2  99.5  98.5 97.0 96.4 96.4 Form. 160.0 * * * * * 84.8 84.8 84.8 84.8 Form. 17 0.0 * * * 5.5 8.2 10.9 16.416.4 16.4 Form. 18 0.0 * * * * * 3.9 5.8 5.8 7.7 Form. 19 0.0 0.0 0.00.0 0.0 0.0 0.0 0.0 0.0 0.0

Experiment 4

As shown in Table 7 below, a formulation (Formulation 22) in which theratio between water and dimethylsilicone oil was 50:50 and the ratiobetween dispersion stabilizer I and dispersion stabilizer II was 0.7:0.3was prepared as a standard. Based on this standard, the ratio betweenwater and dimethylsilicone oil was varied, and further the amount ofdispersion stabilizer I was increased or reduced in accordance with anincrease or decrease in the amount of water, respectively, and theamount of dispersion stabilizer II was increased or reduced inaccordance with an increase or decrease in the amount ofdimethylsilicone oil, respectively, to prepare various emulsions. Foreach emulsion, the water separation rate was measured. The results areshown in Table 8 below and FIG. 5. The evaluation of each of theemulsions is shown also in Table 7.

From the results shown in Table 8 and FIG. 5, it can be understood thatFormulations 21 to 24 produce emulsions with a desirable waterdispersion stability. TABLE 7 Compositions of Formulations 20-24 and theResults of Evaluation Form. Form. Form. Form. Form. 20 21 22 23 24Dimethyl- 10 30 50 70 90 silicone oil Water 90 70 50 30 10 Dispersion1.26 0.98 0.7 0.42 0.14 stabilizer I Dispersion 0.06 0.18 0.3 0.42 0.54stabilizer II Evaluation X ◯ ◯ ◯ ◯

TABLE 8 Water Separation Rates of Formulations 20-24 Water SeparationRate (%) After After After After After After After After After After 0.5min. 1 min. 2 min. 3 min. 5 min. 7 min. 10 min. 12 min. 15 min. 20 min.Form. 20 0.0 94.5  87.3  87.3  87.3  87.3  87.3  87.3  87.3  87.3  Form.21 0.0 * * * 7.7 7.7 7.7 9.7 16.3  17.0  Form. 22 0.0 * * * 5.5 8.210.9  16.4  16.4  16.4  Form. 23 0.0 * * * 9.0 10.8  18.1  22.6  36.1 Form. 24 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Experiment 5

As shown in Table 9 below, various emulsions (Formulations 25-29) wereprepared in which the ratio between dimethylsilicone oil and water wasvaried while fixing the total amount of these at constant, and theamount of dispersion stabilizer I was changed in accordance with anincrease or decrease in amount of water, with the ratio betweendispersion stabilizer I and stabilizer II fixed at constant. For eachemulsion, the water separation rate was measured. The results are shownin Table 10 below and FIG. 6. The evaluation of each of the emulsions isshown also in Table 9.

From the results shown in Table 10 and FIG. 6, it can be understood thatas the ratio of water is higher, the dispersion property of water islowered. It can be further understood that Formulations 26 to 29 produceemulsions with a desirable water dispersion stability. TABLE 9Compositions of Formulations 25-29 and the Results of Evaluation Form.Form. Form. Form. Form. 25 26 27 28 29 Dimethyl- 10 30 50 70 90 siliconeoil Water 90 70 50 30 10 Dispersion 1.26 0.98 0.7 0.42 0.14 stabilizer IDispersion 0.54 0.42 0.3 0.18 0.06 stabilizer II Evaluation X ◯ ◯ ◯ ◯

TABLE 10 Water Separation Rates of Formulations 25-29 Water SeparationRate (%) After After After After After After After After After After 0.5min. 1 min. 2 min. 3 min. 5 min. 7 min. 10 min. 12 min. 15 min. 20 min.Form. 25 0.0 * * * * * * * * 96.3  Form. 26 0.0 * * 5.8 5.8 7.0 7.0 7.78.5 9.7 Form. 27 0.0 * * * 5.5 8.2 10.9  16.4  16.4  16.4  Form. 280.0 * * * 0.0 0.0 13.5  20.8  27.1  Form. 29 0.0 0.0 0.0 0.0 0.0 0.0 0.00.0 0.0 0.0

The results of the Experiments described above collectively show thatthe amounts of water, dimethylsilicone oil, dispersion stabilizers I andII in those emulsions that have desirable water dispersion stabilitiesare as shown in Table 11 below. TABLE 11 Desirable Composition Dimethyl-Dispersion Dispersion silicone stabilizer stabilizer oil Water I IIExperiment 50 50 0.5-0.7 0.3-0.5 1 Experiment 50 50 0.35-1.4  0.15-0.6 2 Experiment 10-50 50-90 0.7 0.3 3 Experiment 10-70 30-90 0.14-0.980.18-0.54 4 Experiment 10-70 30-90 0.14-0.98 0.06-0.42 5

Thus, it is seen that those water-in-oil emulsions that contain 100parts by weight of the liquid silicone rubber material, 0.15 to 3.5parts by weight of the first ether-modified silicone oil, 0.05 to 2parts by weight of the second ether-modified silicone oil (the totalamount of the dispersion stabilizers: 0.2 to 55 parts by weight) and 10to 250 parts by weight of water exhibit excellent water dispersionstabilities. It has been confirmed that these optimal amounts of thesecomponents that were obtained from the results of the above-describedExperiments well agrees with that of the case where a curable liquidsilicone rubber material (for example, a combination of polysiloxanehaving unsaturated aliphatic groups and silicone oil having activehydrogen) was actually used in practice.

Experiment 6

As shown in Table 12 below, various emulsions were prepared in whichdispersion stabilizers A to E were blended solely while fixing the ratiobetween and the total amount of dimethylsilicone oil and water atconstant. For each emulsion, the water separation rate was measured. Theresults are shown in Table 13 below and FIG. 7. The evaluation of eachof the emulsions is shown also in Table 12. It should be noted that withFormulation 30, a portion of the oil gelled as in the case ofFormulation 5. TABLE 12 Compositions of Formulations 30-34 and theResults of Evaluation HLB Form. Form. Form. Form. Form. value 30 31 3233 34 Dimethyl- 50 50 50 50 50 silicone oil Water 50 50 50 50 50Dispersion 4 1 stabilizer A Dispersion 7 1 stabilizer B Dispersion 10 1stabilizer C Dispersion 11 1 stabilizer D Dispersion 16 1 stabilizer EEvaluation X X X X X

TABLE 13 Water Separation Rates of Formulations 31-34 Water SeparationRate (%) After After After After After After After After After After 0.5min. 1 min. 2 min. 3 min. 5 min. 7 min. 10 min. 12 min. 15 min. 20 min.Form. 31 0.0 * 16.3 24.4 37.9 51.5 58.2 60.9 62.3 66.6 Form. 32 0.0 *7.0 11.9 20.3 22.8 37.9 46.0 51.5 56.9 Form. 33 0.0 5.5 9.8 16.4 24.638.3 41.0 43.8 49.2 54.7 Form. 34 0.0 10.8  21.7 27.1 41.7 51.5 53.154.2 56.9 59.6

As is clear from the results shown in Table 13 and FIG. 7, it can beunderstood that with any one of Formulations 30 to 34, an emulsion thatsatisfies a desirable standard of a water separation rate of 50% or lessafter 20 minutes cannot be obtained.

Experiment 7

As shown in Table 14 below, various emulsions (Formulations 35-38) wereprepared in which the ratio and the total amount of dimethylsilicone oiland water was fixed at constant and the amount of dispersion stabilizerA was fixed at constant, and further, dispersion stabilizers B to E wereblended. For each emulsion, the water separation rate was measured. Theresults are shown in Table 15 below and FIG. 8. The evaluation of eachof the emulsions is shown also in Table 14. TABLE 14 Compositions ofFormulations 35-38 and the Results of Evaluation HLB Form. Form. Form.Form. value 35 36 37 38 Dimethyl- 50 50 50 50 silicone oil Water 50 5050 50 Dispersion 4 0.5 0.5 0.5 0.5 stabilizer A Dispersion 7 0.5stabilizer B Dispersion 10 0.5 stabilizer C Dispersion 11 0.5 stabilizerD Dispersion 16 0.5 stabilizer E Evaluation ◯ ◯ ◯ X

TABLE 15 Water Separation Rates of Formulations 35-38 Water SeparationRate (%) After After After After After After After After After After 0.5min. 1 min. 2 min. 3 min. 5 min. 7 min. 10 min. 12 min. 15 min. 20 min.Form. 0.0 * * * 5.4 10.8 11.9 15.2 16.3 21.7 35 Form. 0.0 * * * 5.4 5.46.0 7.6 8.1 9.8 36 Form. 0.0 * * * * 8.2 16.4 21.9 21.9 21.9 37 Form.0.0 10.8  97.5  97.5  97.5  97.5 97.5 97.5 97.5 97.5 38

As can be understood from the results shown in Table 15 and FIG. 8, itcan be understood that Formulations 35 to 37 produce emulsions with adesirable water dispersion stability.

Experiment 8

As shown in Table 16 below, various emulsions (Formulations 39-41) wereprepared in which the ratio and the total amount of dimethylsilicone oiland water were fixed at constant and the amount of dispersion stabilizerB was fixed at constant, and further, dispersion stabilizers C to E wereblended. For each emulsion, the water separation rate was measured. Theresults are shown in Table 17 below and FIG. 9. The evaluation of eachof the emulsions is shown also in Table 16. TABLE 16 Compositions ofFormulations 39-41 and the Results of Evaluation HLB Form. Form. Form.value 39 40 41 Dimethyl- 50 50 50 silicone oil Water 50 50 50 Dispersion4 stabilizer A Dispersion 7 0.5 0.5 0.5 stabilizer B Dispersion 10 0.5stabilizer C Dispersion 11 0.5 stabilizer D Dispersion 16 0.5 stabilizerE Evaluation X ◯ X

TABLE 17 Water Separation Rates of Formulations 39-41 Water SeparationRate (%) After After After After After After After After After After 0.5min. 1 min. 2 min. 3 min. 5 min. 7 min. 10 min. 12 min. 15 min. 20 min.Form. 39 0.0 * 8.1 10.3 16.3 25.5 32.5 37.9 46.0 54.2 Form. 40 0.0 8.110.8 13.5 19.0 24.4 37.9 42.3 48.8 49.8 Form. 41 0.0 10.8  21.7 29.843.3 54.2 62.3 62.3 65.0 65.0

As can be understood from the results shown in Table 17 and FIG. 9, itcan be understood that Formulation 40 produces an emulsion with adesirable water dispersion stability.

Experiment 9

As shown in Table 18 below, various emulsions (Formulations 42-43) wereprepared in which the ratio and the total amount of dimethylsilicone oiland water were fixed at constant and the amount of dispersion stabilizerC was fixed at constant, and further, dispersion stabilizers D to E wereblended. For each emulsion, the water separation rate was measured. Theresults are shown in Table 19 below and FIG. 10. The evaluation of eachof the emulsions is shown also in Table 18. TABLE 18 Compositions ofFormulations 42-43 and the Results of Evaluation HLB value Form. 42Form. 43 Dimethyl- 50 50 silicone oil Water 50 50 Dispersion 4stabilizer A Dispersion 7 stabilizer B Dispersion 10 0.5 0.5 stabilizerC Dispersion 11 0.5 stabilizer D Dispersion 16 0.5 stabilizer EEvaluation X X

TABLE 19 Water Separation Rates of Formulations 42-43 Water SeparationRate (%) After After After After After After After After After After 0.5min. 1 min. 2 min. 3 min. 5 min. 7 min. 10 min. 12 min. 15 min. 20 min.Form. 42 0.0 9.8 21.7 32.5 51.5 59.6 66.1 70.4 73.1 75.8 Form. 43 0.010.8 21.7 29.8 43.3 54.2 62.3 62.3 65.0 65.0

As can be understood from the results shown in Table 19 and FIG. 10, itcan be understood that Formulations 42 to 43 produce emulsions with adesirable water dispersion stability.

From the results obtained above, it can be understood that thedispersion stabilizer is desirably composed of a combination of anether-modified silicone oil having an HLB value of 7 to 11 (especiallyfrom Table 15 and FIG. 8) and another ether-modified silicone oil havingan HLB value of 4 to 7 (especially from Table 17 and FIG. 9), in orderto produce an emulsion having a desirable water dispersion stability. Itcan further be understood that the difference in the HLB value betweenthe two ether-modified silicone oils is at least 3 (=7−4).

EXAMPLE 1

In this Example, a liquid silicone rubber (trade name: KE-1353)available from Shin-Etsu Chemical Co., Ltd was used as a liquid siliconerubber material. This liquid silicone rubber was provided in the form ofseparate packages of an active hydrogen-containing polysiloxane and avinyl group-containing polysiloxane, with a catalytic amount of platinumcatalyst added to the vinyl group-containing polysiloxane. Hereinafter,the former will be referred to as “silicone rubber precursor A”, and thelatter will be referred to as “silicone rubber precursor B”. The activehydrogen-containing polysiloxane has a structure represented by theabove-described formula (2) in which each R⁴ is a methyl group, whereasthe vinyl group-containing polysiloxane has a structure represented bythe above-described formula (1) in which each R¹ is a vinyl group andeach R² is a methyl group. As the dispersion stabilizers, dispersionstabilizers I and II used in Experiments 1 to 5 described above wereused.

A mixture of 0.7 parts by weight of dispersion stabilizer I and 0.3parts by weight of dispersion stabilizer II premixed in advance wasadded to 50 parts by weight of the silicone rubber precursor A, and theresultant mixture was stirred for 5 minutes with a hand mixer to have itfully dispersed, thereby preparing a mixture A. On the other hand, amixture of 0.7 parts by weight of dispersion stabilizer I and 0.3 partsby weight of dispersion stabilizer II premixed in advance was added to50 parts by weight of the silicone rubber precursor B, and the resultantmixture was stirred for 5 minutes with a hand mixer to have it fullydispersed, thereby preparing a mixture B.

The mixtures A and B thus obtained were mixed together. Then, whilestirring the resultant mixture for three minutes with a hand mixer, 10parts by weight of water was added thereto and the mixture was furtherstirred for 2 minutes. While stirring the mixture with a hand mixer, 90parts by weight of water was gradually added, thereby preparing anemulsion.

The emulsion thus obtained was defoamed in a vacuum decompressor toremove the air entrained in the emulsion. Then, it was poured into acompression mold having a depth of 6 mm, and heated using a stampingdisk at a temperature of 100° C. for 30 minutes (primary heating) tomold it. The molded body thus obtained (porous material precursor) washeated in an electric furnace at 150° C. for 5 hours (secondary heating)to remove the water. Thus, a silicone elastomer porous material testpiece having a rectangular solid portion with a length of 42 mm, a widthof 20 mm and a thickness of 6 mm. This test piece was cut in its widthdirection, and the cross section was observed under an SEM. Theobservation area was 56517.301 μm². In the observation under the SEM, 52cells (pores) were detected. The maximum cell diameter was 44.14 μm, theminimum cell diameter was 19.94 μm, and the average cell diameters was19.94 μm with a standard deviation of 9.35. A photograph of the crosssection of the test piece taken under the SEM (magnification of 200times) is shown in FIG. 11. As shown, the water-in-oil emulsion canproduce a closed-cell porous material having very fine cells of evendiameter.

EXAMPLE 2

In this Example, a liquid silicone rubber (trade name: DY35-7002)available from Dow Corning Torey Silicone Ltd. was used as a liquidsilicone rubber material. This liquid silicone rubber was provided inthe form of separate packages of an active hydrogen-containingpolysiloxane and a vinyl group-containing polysiloxane, with a catalyticamount of platinum catalyst added to the vinyl group-containingpolysiloxane. Hereinafter, the former will be called silicone rubberprecursor A, and the latter will be called silicone rubber precursor B.The active hydrogen-containing polysiloxane has a structure representedby the above-described formula (2) in which each R⁴ is a methyl group,whereas the vinyl group-containing polysiloxane has a structurerepresented by the above-described formula (1) in which each R¹ is avinyl group and each R² is a methyl group. As the dispersionstabilizers, dispersion stabilizers I and II used in Experiments 1 to 5described above were used.

A mixture of 0.7 parts by weight of dispersion stabilizer I and 0.3parts by weight of dispersion stabilizer II premixed in advance wasadded to 50 parts by weight of the silicone rubber precursor A, and theresultant mixture was stirred for 5 minutes with a hand mixer to have itfully dispersed, thereby preparing a mixture A. On the other hand, amixture of 0.7 parts by weight of dispersion stabilizer I and 0.3 partsby weight of dispersion stabilizer II premixed in advance was added to50 parts by weight of the silicone rubber precursor B, and the resultantmixture was stirred for 5 minutes with a hand mixer to have it fullydispersed, thereby preparing a mixture B.

The mixtures A and B thus obtained were mixed together. Then, whilestirring the resultant mixture for three minutes with a hand mixer, 10parts by weight of water was added thereto and the mixture was furtherstirred for 2 minutes. While stirring the mixture with a hand mixer, 90parts by weight of water was gradually added, thereby preparing anemulsion.

From the emulsion thus obtained, a silicone elastomer porous materialtest piece was obtained as in Example 1.

This test piece was cut in its width direction, and the cross sectionwas observed under an SEM. The observation area was 55656.641 μm². Inthe observation under the SEM, 686 cells (pores) were detected. Themaximum cell diameter was 22.215 μm, the minimum cell diameter was 3.405μm, and the average cell diameters was 4.657 μm with a standarddeviation of 1.306. A photograph of the cross section of the test piecetaken under the SEM (magnification of 200 times) is shown in FIG. 12. Asshown, the water-in-oil emulsion produces a closed-cell porous materialhaving very fine cells of even diameter.

COMPARATIVE EXAMPLE 1

In this comparative Example, no dispersion stabilizers were used. Thus,50 parts by weight of silicone rubber precursor A of Example 1 was addedto 50 parts by weight of silicone rubber precursor B of Example 1, andthe mixture was stirred with a hand mixer for 5 minutes. 10 parts byweight of water was added to the resultant mixture, which was stirredfor 2 minutes. Then, 90 parts by weight of water was additionally addedto form an emulsion; however, water was separated from the siliconerubber, and the emulsion was not formed. With this mixture, no moldingcould be done.

Then, the amount of additional water was reduced to 40 parts by weight,and an emulsion was tried to form, but the emulsion could not be made asabove. However, a test piece could be made under the same conditions asin Example 1. A photograph of the cross section of this test piece takenunder the SEM (magnification of 200 times) is shown in FIG. 13.

As can be understood from the results obtained here, it has beenconcluded that without using a dispersion stabilizer, an emulsion cannotbe prepared. Further, the obtained mold body has cells with largediameters, and the diameter varies greatly from a cell to another.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and embodiments shown and describedherein. Accordingly, various modifications may be made without departingfrom the spirit or scope of the general inventive concept as defined bythe appended claims and their equivalents.

1. A method of preparing a silicone elastomer porous material,comprising: providing a water-in-oil emulsion comprising a liquidsilicone rubber material which forms a silicone elastomer upon curing, asilicone oil material which has a surface activation function, and waterdroplets dispersed in the liquid silicone rubber material; subjectingthe emulsion to a primary heating, thereby curing the liquid siliconerubber material to form a silicone elastomer and confining the waterdroplets within the silicone elastomer substantially as they are presentin the emulsion; and subjecting the silicone elastomer confining thewater droplets therein to a secondary heating, thereby evaporating andremoving the water droplets from the silicone elastomer, thereby formingthe silicone elastomer porous material.
 2. The method according to claim1, wherein the primary heating is carried out at 80 to 130° C. for about5 to 60 minutes.
 3. The method according to claim 2, wherein thesecondary heating is carried out at 70 to 300° C. for about 1 to 24hours.
 4. The method according to claim 1, wherein the liquid siliconerubber material is an addition reaction curing one.
 5. The methodaccording to claim 4, wherein the liquid silicone rubber materialincludes a polysiloxane having an unsaturated aliphatic group and apolysiloxane having active hydrogen.
 6. The method according to claim 5,wherein the unsaturated aliphatic group is a vinyl group.
 7. The methodaccording to claim 1, wherein the silicone oil material has ahydrophilic group.
 8. The method according to claim 1, wherein thesilicone oil material comprises a mixture of a first silicone oil and asecond silicone oil, and a difference in HLB value between the firstsilicone oil and the second silicone oil is at least
 3. 9. The methodaccording to claim 7, wherein the silicone oil material comprises amixture of a first ether-modified silicone oil and a secondether-modified silicone oil, and a difference in HLB value between thefirst ether-modified silicone oil and the second ether-modified siliconeoil is at least
 3. 10. The method according to claim 9, wherein thefirst ether-modified silicone oil has an HLB value of 7 to 11 and thesecond ether-modified silicone oil has an HLB value of 4 to
 7. 11. Themethod according to claim 1, wherein the emulsion composition comprises100 parts by weight of the liquid silicone rubber material, 0.2 to 5.5parts by weight weight of the silicone oil material, and 10 to 250 partsby weight of the water droplets.
 12. The method according to claim 8,wherein the emulsion composition comprises 100 parts by weight of theliquid silicone rubber material, 0.15 to 3.5 parts by weight of thefirst silicone oil, 0.05 to 2 parts by weight of the second siliconeoil, and 10 to 250 parts by weight of the water droplets.
 13. The methodaccording to claim 9, comprising 100 parts by weight of the liquidsilicone rubber material, 0.15 to 3.5 parts by weight of the firstether-modified silicone oil, 0.05 to 2 parts by weight of the secondether-modified silicone oil, and 10 to 250 parts by weight of the waterdroplets.
 14. The method according to claim 1, wherein the waterdroplets has an average diameter of 1 to 50 μm.